Display screen or portion thereof with a graphical user interface for an on-board device



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface for an on-board device, showing our new design.

The outermost broken-lines rectangle shows a display screen or a portion thereof and forms no part of the claimed design. The remaining broken lines illustrate portions of a graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface for an on-board device, as shown and described. 